EP3909924B1 - Glass sheet with high transmission of infrared radiation - Google Patents

Description

1. Field of the invention

The present invention relates to a glass sheet having high transmission to infrared radiation.

The invention also relates to the use of such a glass sheet in a device using infrared radiation propagating essentially inside said sheet.

Thanks to its high transmission of infrared (IR) radiation, the glass sheet according to the invention can in fact be advantageously used, for example, in a touch screen or panel or tablet (“touchscreen” or “touchpanel” or “touchpad” ) using optical technology called “Planar Scatter Detection” (PSD) or “Frustrated total internal reflection” (FTIR) (or any other technology requiring high IR transmission) to detect the position of one or more objects ( for example, a finger or a stylus) on a surface of said sheet.

The invention therefore also relates to a screen, a panel or a touch pad comprising such a sheet of glass.

2. Prior art solutions

PSD and FTIR technologies enable multi-sensing touch screens/panels that are inexpensive and can have a relatively large touch area (e.g., 3 to 100 inches) while having a low thickness.

1. (i) l'injection d'un rayonnement infrarouge (IR), grâce à des LED's par exemple, dans un substrat transparent aux infrarouges à partir d'un ou plusieurs bords/tranches ;
2. (ii) la propagation du rayonnement infrarouge à l'intérieur dudit substrat (qui joue alors le rôle de guide d'onde), par l'intermédiaire d'un phénomène optique de réflexion totale interne (aucun rayonnement ne « sort » du substrat);
3. (iii) le contact de la surface du substrat avec un objet quelconque (par exemple, un doigt ou un stylet) entraînant une perturbation locale par diffusion du rayonnement dans toutes les directions ; certains des rayons déviés vont ainsi pouvoir « sortir » du substrat.

These two technologies involve:

1. (i) the injection of infrared (IR) radiation, using LEDs for example, into an infrared transparent substrate from one or more edges/slices;
2. (ii) the propagation of infrared radiation inside said substrate (which then plays the role of waveguide), via an optical phenomenon of total internal reflection (no radiation “comes out” of the substrate) ;
3. (iii) contact of the surface of the substrate with any object (for example, a finger or a stylus) resulting in local disturbance by diffusion of radiation in all directions; some of the deflected rays will thus be able to “exit” the substrate.

In FTIR technology, the deflected rays form an infrared light spot on the lower surface of the substrate, opposite the touch surface. These are seen by a special camera located underneath the device.

• (iv) l'analyse par un détecteur du rayonnement IR résultant au niveau du bord du substrat; et
• (v) le calcul par des algorithmes de la/des position(s) du/des objet(s) en contact avec la surface, à partir du rayonnement détecté. Cette technologie est notamment exposée dans le document US2013021300A1 .

PSD technology involves two additional steps following steps (i)-(iii):

• (iv) analyzing the resulting IR radiation at the edge of the substrate by a detector; And
• (v) calculation by algorithms of the position(s) of the object(s) in contact with the surface, from the detected radiation. This technology is notably exposed in the document US2013021300A1 .

Basically, glass is a material of choice for touch panels because of its mechanical properties, its durability, its scratch resistance, its optical clarity and because it can be chemically or thermally reinforced.

In the case of glass panels used for PSD or FTIR technology and of very large surface area and therefore of relatively large length/width, the optical path of the injected IR radiation is long. In this case, the absorption of IR radiation by the glass material therefore significantly affects the sensitivity of the touch panel which can then decrease undesirably in the length/width of the panel. In the case of glass panels used for PSD or FTIR technology and with a smaller surface area and therefore with a shorter optical path of the injected IR radiation, the absorption of the IR radiation by the glass material also plays a role, in particular on the energy consumption of the device integrating the glass panel.

Thus, a sheet of glass highly transparent to infrared radiation is of great use in this context, in order to guarantee intact or sufficient sensitivity over the entire tactile surface when this surface is large. In particular, a sheet of glass with an absorption coefficient at the wavelength of 1050 nm, generally used in these technologies, is sought as low as possible.

In order to obtain high transmission in the infrared (and in the visible), it is known to reduce the total iron content in the glass (expressed in terms of Fe ₂ O ₃ according to standard practice in the field) by obtaining glasses with low iron content (or “low iron”). Silicate type glasses always contain iron because it is present as an impurity in most of the raw materials used (sand, limestone, dolomite, etc.). Iron exists in the glass structure in the form of ferric Fe ³⁺ ions and ferrous Fe ²⁺ ions. The presence of ferric Fe ³⁺ ions gives the glass a slight absorption of visible light of short wavelength and a stronger absorption in the near ultraviolet (absorption band centered on 380 nm), while the presence of Ferrous Fe ²⁺ ions (sometimes expressed as FeO oxide) cause strong absorption in the near infrared (absorption band centered on 1050 nm). Thus, increasing the total iron content (in its two forms) accentuates absorption in the visible and infrared. In addition, a high concentration of ferrous Fe ²⁺ ions leads to a decrease in infrared transmission (in particular, near infrared). However, to achieve an absorption coefficient at the wavelength of 1050 nm sufficiently low for tactile applications only by varying the total iron content, this would require such a significant reduction in this total iron content that (i ) either this would lead to production costs that are much too high, coming from the need for very pure raw materials (which sometimes do not even exist sufficiently pure), (ii) or this would pose production problems (in particular premature wear of the oven and/or difficulty heating the glass in the oven).

It is also known, to further increase the transmission of glass, to oxidize the iron present in the glass, that is to say to reduce the ion content ferrous in favor of the ferric ion content. The degree of oxidation of a glass is given by its redox, defined as the ratio by weight of Fe ²⁺ atom to the total weight of iron atoms present in the glass, Fe ²⁺ /total Fe.

In order to reduce the redox of glass, it is known to add an oxidizing component to the batch of raw materials. However, most of the known oxidants (sulphates, nitrates, etc.) have an oxidizing power which is not strong enough to achieve the IR transmission values sought for the application of touch panels using FTIR or PSD technology or must be added in too large a quantity with collateral disadvantages such as cost, coloring, incompatibility with the production process, etc.

The document US2007/161492 discloses colored glass compositions and, in particular, Examples 1-4 of glass compositions comprising iron and chromium. The document US2013/021300 is directed towards improving the performance of FTIR tactile systems without affecting the optical qualities of the system.

3. Objectives of the invention

The invention, in at least one of its embodiments, aims to provide a sheet of glass with high transmission to infrared radiation. In particular, the invention aims to provide a sheet of glass with high transmission to near infrared radiation.

The invention, in at least one of its embodiments, aims to provide a sheet of glass with high transmission to infrared radiation which is in particular particularly valuable in a device using infrared radiation propagating essentially inside the said sheet.

Another objective of the invention, in at least one of its embodiments, is to provide a sheet of glass which, when used as a touch surface in large touch screens, panels or tablets, does not cause no or little loss of sensitivity of the touch function.

Another objective of the invention, in at least one of its embodiments, is to provide a sheet of glass which, when used as a touch surface in screens, panels or touch tablets of more modest dimensions, is favorable to the energy consumption of the device.

Another objective of the invention, in at least one of its embodiments, is to provide a sheet of glass with high transmission to infrared radiation and with acceptable aesthetics for the chosen application.

Finally, the invention also aims to provide a sheet of glass with high transmission to infrared radiation and which is inexpensive to produce.

4. Presentation of the invention

The invention relates to a sheet of glass having a composition which comprises, in a content expressed as percentages by total weight of glass: SiO ₂ 60 - 75% Al ₂ O ₃ 0 - 4% B ₂ O ₃ 0 - 4% Na ₂ O 5 - 20% CaO 1 - 15% MgO 0 - 10% K ₂ O 0 - 10% BaO 0 - 5% Total iron expressed as Fe ₂ O ₃ 0.002 - 0.02% and an Fe ²⁺ content expressed as FeO, less than 20ppm.

In accordance with a particular embodiment, said composition further comprises a chromium content such as: 0.0001% < Cr ₂ O ₃ < 0.002%, expressed as percentages by total weight of glass.

Thus, the invention is based on a completely new and inventive approach because it makes it possible to solve the technical problem posed. The inventors have in fact demonstrated, in a surprising manner, that it was possible, by combining in a glass composition a low iron content and chromium, especially known as a powerful dye in so-called “colored glass” compositions. selective", in a specific range of contents, to obtain a sheet of glass that is very transparent in the IR, without too negative an impact on its aesthetics and its color.

Throughout this text, when a range is indicated, unless explicitly stated, the ends are included. Additionally, all integer values and subdomains in a numeric range are expressly included as if explicitly written. Also throughout this text, unless explicitly stated, the percentage content values are weight values, expressed in relation to the total weight of the glass.

Other characteristics and advantages of the invention will appear more clearly on reading the following description.

By glass within the meaning of the invention, we mean a completely amorphous material, therefore excluding any crystalline material, even partially (such as for example, glass-crystalline or glass-ceramic materials).

For reasons of lower production costs, the sheet of glass according to the invention is a sheet of silico-soda-lime glass. The sheet of glass according to the invention may be a sheet of glass obtained by a process of floating, drawing, rolling or any other known process for manufacturing a sheet of glass starting from a molten glass composition. According to a preferred embodiment according to the invention, the sheet of glass is a sheet of float glass. By sheet of float glass, we mean a sheet of glass formed by the flotation process (or “float”), consisting of pouring the molten glass onto a bath of molten tin, under reducing conditions. A sheet of float glass has, in a known manner, a face called a “tin face”, that is to say a face enriched with tin in the mass of the glass close to the surface of the sheet. By tin enrichment is meant an increase in the tin concentration relative to the composition of the core glass which may or may not be substantially zero (tin-free).

According to the invention, different chromium-containing raw materials can be used to introduce chromium into the glass composition. In particular, the chromium oxides CrO, Cr ₂ O ₃ , CrO ₂ or CrO ₃ are possible and relatively pure sources of chromium. Other substances rich in chromium can also be used, such as chromates, chromites or any other chromium-based chemical compound. Compounds containing chromium in its 6+ form are, however, less preferred for safety reasons.

The glass sheet according to the invention can have various and relatively large dimensions. It can, for example, have dimensions of up to 3.21 m x 6 m or 3.21 m x 5.50 m or 3.21 m x 5.10 m or 3.21 m x 4.50 m (sheet of glass called “PLF”) or, for example, 3.21 m x 2.55 m or 3.21 m x 2.25 m (sheet of glass called “DLF”).

The glass sheet according to the invention can have a thickness varying between 0.1 and 25 mm. Advantageously, in the case of the application of touch panels, the sheet of glass according to the invention can have a thickness varying between 0.1 and 6mm. Preferably, in the case of the application of touch screens, for weight reasons, the thickness of the glass sheet according to the invention is 0.1 to 2.2 mm.

According to the invention, the composition of the invention comprises a total iron content (expressed in terms of Fe ₂ O ₃ ) ranging from 0.002 to 0.02% by weight relative to the total weight of the glass. A total iron content (expressed in the form of Fe ₂ O ₃ ) less than or equal to 0.02% by weight makes it possible to further increase the IR transmission of the glass sheet. The minimum value makes it possible not to penalize the cost of the glass too much because such low iron values often require very pure, expensive raw materials or even purification of these. Preferably, the composition comprises a total iron content (expressed in the form of Fe ₂ O ₃ ) ranging from 0.002 to 0.01% by weight relative to the total weight of the glass.

According to an advantageous embodiment of the invention, the composition of the invention has a chromium/total iron ratio such that: 0.05 ≤ Cr ₂ O ₃ /Fe ₂ O ₃ ≤ 1. According to this embodiment and preferred manner, the composition has a chromium/total iron ratio such that 0.1 < Cr ₂ O ₃ /Fe ₂ O ₃ ≤ 1. Such a range of chromium/total iron ratio makes it possible to obtain significant transmission in the IR without overly penalizing the aesthetic appearance, the coloring of the glass sheet. Most preferably, the composition has a chromium/total iron ratio such that 0.15 ≤ Cr ₂ O ₃ /Fe ₂ O ₃ ≤ 1. Alternatively, the composition has a chromium/total iron ratio such that 0.1 < Cr ₂ O ₃ /Fe ₂ O ₃ ≤ 0.5.

According to a particularly advantageous embodiment of the invention, the composition comprises a chromium content such as: 0.0005% ≤ Cr ₂ O ₃ < 0.002%. Most preferably, the composition of the invention comprises a chromium content such as: 0.001% <Cr ₂ O ₃ <0.002%. Such a range of chromium contents makes it possible to obtain improved transmission in the IR.

According to the invention, the composition comprises an Fe ²⁺ content (expressed in the form of FeO) of less than 20 ppm. This range of contents makes it possible to obtain very satisfactory properties, in particular in terms of IR transmission. Preferably, the composition comprises a content of Fe ²⁺ (expressed as FeO) less than 10 ppm. Most preferably, the composition comprises an Fe ²⁺ content (expressed in the form of FeO) of less than 5 ppm.

According to the invention, the glass sheet has a high transmission of IR radiation. More specifically, the glass sheet of the present invention has a high transmission of near-infrared radiation. To quantify the good transmission of glass in the infrared domain, in the present description, we will use the absorption coefficient at the wavelength of 1050 nm, which must therefore be as low as possible in order to obtain good transmission. The absorption coefficient is defined by the ratio between the absorbance and the length of the optical path traveled by electromagnetic radiation in a given medium. It is expressed in m ^-1 . It is therefore independent of the thickness of the material but it depends on the wavelength of the absorbed radiation and the chemical nature of the material.

avec $$\mathrm{\rho }={\left(\mathrm{n}-1\right)}^2/{\left(\mathrm{n}+1\right)}^2$$

In the case of glass, the absorption coefficient ( µ ) at a chosen wavelength λ can be calculated from a transmission measurement ( T ) as well as the refractive index n of the material ( thick = thickness), the values of n, ρ and T being a function of the chosen wavelength λ: $$\mathrm{\mu }=-\frac{1}{\mathit{thick}}.\mathit{ln}\left[\frac{-{\left(1-\rho \right)}^2+\sqrt{{\left(1-\rho \right)}^4+4.T^2{\rho }^2}}{2.T.{\rho }^2}\right]$$

with $$\mathrm{\rho }={\left(\mathrm{not}-1\right)}^2/{\left(\mathrm{not}+1\right)}^2$$

Advantageously, the glass sheet according to the invention has an absorption coefficient at the wavelength of 1050 nm less than or equal to 5 m ^-1 . Preferably, the glass sheet according to the invention has an absorption coefficient at the wavelength of 1050 nm less than or equal to 3.5 m ^-1 . Most preferably, the glass sheet according to the invention has an absorption coefficient at the wavelength of 1050 nm less than or equal to 2 m ^-1 . Even more preferably, the glass sheet according to the invention has an absorption coefficient at the wavelength of 1050 nm less than or equal to 1 m ^-1 .

Advantageously, the glass sheet according to the invention has an absorption coefficient at the wavelength of 950 nm less than or equal to 5 m ^-1 . Preferably, the glass sheet according to the invention has an absorption coefficient at the wavelength of 950 nm less than or equal to 3.5 m ^-1 . Most preferably, the glass sheet according to the invention has an absorption coefficient at the wavelength of 950 nm less than or equal to 2 m ^-1 . Even more preferably, the glass sheet according to the invention has an absorption coefficient at the wavelength of 950 nm less than or equal to 1 m ^-1 . Advantageously, the glass sheet according to the invention has a absorption coefficient at the wavelength of 850 nm less than or equal to 5 m ^-1 . Preferably, the glass sheet according to the invention has an absorption coefficient at the wavelength of 850 nm less than or equal to 3.5 m ^-1 . Most preferably, the glass sheet according to the invention has an absorption coefficient at the wavelength of 850 nm less than or equal to 2 m ^-1 . Even more preferably, the glass sheet according to the invention has an absorption coefficient at the wavelength of 850 nm less than or equal to 1 m ^-1 .

According to one embodiment of the invention, the composition of the glass sheet may comprise, in addition to the impurities contained in particular in the raw materials, a small proportion of additives (such as agents helping the melting or refining of the glass) or elements coming from the dissolution of the refractories constituting the melting furnaces.

According to one embodiment of the invention, the composition of the glass sheet may also comprise one or more dye(s), in quantities adapted depending on the desired effect. This(these) dye(s) can be used, for example, to “neutralize” the color generated by the presence of chromium and thus make the coloring of the glass of the invention more neutral, colorless. Alternatively, these dyes can be used to obtain a desired color other than that which can be generated by the presence of chromium.

According to another advantageous embodiment of the invention, combinable with the previous embodiment, the glass sheet can be coated with a layer or a film which makes it possible to modify or neutralize the color which can be generated by the presence of the chrome (for example, colored PVB film).

The glass sheet according to the invention can advantageously be chemically or thermally tempered.

According to one embodiment of the invention, the glass sheet is coated with at least one thin transparent and electrically conductive layer. A transparent and conductive thin layer according to the invention can, for example, be a layer based on SnO ₂ :F, SnO ₂ :Sb or ITO (indium tin oxide), ZnO:Al or again ZnO:Ga.

According to another advantageous embodiment of the invention, the glass sheet is coated with at least one anti-reflective (or anti-reflective) layer. This embodiment is obviously advantageous in the case of using the glass sheet of the invention as the front face of a screen. An antireflective layer according to the invention can, for example, be a layer based on porous silica with a low refractive index or it can consist of several layers (stack), in particular a stack of layers of dielectric material alternating layers with low and high refractive indices and ending with a low refractive index layer.

According to another embodiment, the glass sheet is coated with at least one anti-fingerprint layer or has been treated so as to reduce/prevent fingerprints from being marked. This embodiment is also advantageous in the case of using the glass sheet of the invention as the front face of a touch screen. Such a layer or such a treatment can be combined with a thin transparent and electrically conductive layer, deposited on the opposite face. Such a layer can be combined with an anti-reflective layer deposited on the same face, the anti-fingerprint layer being outside the stack and therefore covering the anti-reflective layer.

According to yet another embodiment, the glass sheet is coated with at least one layer (or has been treated) so as to reduce or prevent reflections and/or the sparkling phenomenon. This embodiment is of course advantageous in the case of using the glass sheet of the invention as the front face of a display device. Such anti-reflective treatment and/or anti-flicker is for example acid matting producing a specific roughness of the treated face of the glass sheet.

Depending on the applications and/or desired properties, other layer(s)/treatment(s) can be deposited/carried out on one and/or the other side of the sheet glass according to the invention.In addition, the invention also relates to a screen or a panel or a tablet, comprising at least one sheet of glass according to the invention, said sheet of glass defining a tactile surface. Preferably, the screen or panel or touch pad uses FTIR or PSD optical technology. In particular, the glass sheet is advantageously mounted above a display surface.

• une teneur en Fer²⁺ exprimée sous forme de FeO, inférieure à 20ppm
• une teneur en chrome telle que : 0,0001%<Cr₂O₃<0,002% ;

dans un dispositif utilisant un rayonnement infrarouge se propageant essentiellement à l'intérieur de ladite feuille. Par rayonnement se propageant essentiellement à l'intérieur de la feuille, on entend un rayonnement qui voyage dans la masse de la feuille de verre entre les deux faces principales de la feuille.Finally, the invention also relates to the use of a sheet of glass having a composition which comprises, in a content expressed as percentages by total weight of glass: SiO ₂ 60 - 75% Al ₂ O ₃ 0 - 4% B ₂ O ₃ 0 - 4% Na ₂ O 5 - 20% CaO 1 - 15% MgO 0 - 10% K ₂ O 0 - 10% BaO 0 - 5% Total iron expressed as Fe ₂ O ₃ 0.002 - 0.02%

• an Iron ²⁺ content expressed in the form of FeO, less than 20ppm
• a chromium content such as: 0.0001% <Cr ₂ O ₃ <0.002%;

in a device using infrared radiation propagating essentially inside said sheet. By radiation propagating essentially inside the sheet, we mean radiation which travels in the mass of the glass sheet between the two main faces of the sheet.

Advantageously, according to one embodiment of the use according to the invention, the propagation of infrared radiation takes place by total internal reflection. According to this embodiment, the infrared radiation can be injected into the interior of the glass sheet from one or more edge(s) of said sheet. By edge of the sheet is meant each of the four surfaces defined by the thickness of the sheet and substantially perpendicular to the two main faces of the sheet. Alternatively, still according to this embodiment, the infrared radiation can be injected inside the glass sheet from one or both main face(s) at a certain angle.

According to another embodiment of the use according to the invention, the composition advantageously has a chromium/total iron ratio such as: 0.05 ≤ Cr ₂ O ₃ /Fe ₂ O ₃ ≤ 1 and preferably, a ratio total chromium/iron such that: 0.1 < Cr ₂ O ₃ /Fe ₂ O ₃ ≤ 1, or again, such that 0.15 ≤ Cr ₂ O ₃ /Fe ₂ O ₃ ≤ 1.

According to another embodiment of the use according to the invention, the composition advantageously has a chromium content such as: 0.0005% ≤ Cr ₂ O ₃ < 0.002% and preferably, a chromium content such as: 0.001% < Cr ₂ O ₃ < 0.002%.

According to another embodiment of the use according to the invention, the composition advantageously comprises a total iron content (expressed in the form of Fe ₂ O ₃ ) of 0.002 to 0.02% by weight relative to the total weight of the glass. and preferably, a total iron content (expressed in the form of Fe ₂ O ₃ ) of 0.002 to 0.01% by weight relative to the total weight of the glass.

The examples which follow illustrate the invention, without the intention of limiting in any way its coverage.

Examples

The raw materials were mixed in powder form and placed in a crucible for fusion, according to the basic composition specified in the table below. Basic composition Content [% by weight] SiO ₂ 72 CaO 8.2 K ₂ O 0.01 Na ₂ O 14 _SO3 0.3 Al ₂ O ₃ 1 MgO 4.5

Different samples were prepared with varying amounts of chromium and iron and the base composition kept fixed. Samples 1 and 5 (comparative) correspond to glasses of the state of the art, with low iron content and without added chromium (and called “extra-clear”) and respectively include 120 and 100 ppm of iron expressed in the form of Fe ₂ O ₃ . Samples 2-4 correspond to glass sheet compositions according to the invention with an iron content of 120 ppm (expressed in the form of Fe ₂ O ₃ ) and samples 6-9 correspond to glass sheet compositions according to the invention with an iron content of 100 ppm (expressed as Fe ₂ O ₃ ).

The optical properties of each glass sample in sheet form were determined and in particular, the absorption coefficient (µ) at wavelengths of 1050, 950 and 850 nm was determined via a transmission measurement on a spectrophotometer. Perkin Elmer lambda 950 equipped with a 150mm diameter integrating sphere, with the sample placed at the entrance port of the sphere for measurement.

The table below presents the variation (Δ) of the absorption coefficient at wavelengths of 1050, 950 and 850 nm obtained for the samples according to the invention, relative to the value for the corresponding sample of reference (without chrome). Sample set A ppm of chromium (expressed as Cr ₂ O ₃ ) ppm iron (expressed as Fe ₂ O ₃ ) Δ absorption coefficient at 1050nm (m-1) Δ absorption coefficient at 950nm (m-1) Δ absorption coefficient at 850nm (m-1) 1 (comparative) 0 (no addition in the mixture) 120 0% 0% 0% 2 3.5 -24% -28% -32% 3 9 -48% -47% -42% 4 13 -56% -60% -66% Sample set B ppm of chromium (expressed as Cr ₂ O ₃ ) ppm iron (expressed as Fe ₂ O ₃ ) Δ absorption coefficient at 1050nm (m-1) Δ absorption coefficient at 950nm (m-1) Δ absorption coefficient at 850nm (m-1) 5 (comparative) 0 (no addition in the mixture) 100 0% 0% 0% 6 3 -22% -20% -18% 7 6.5 -34% -35% -38% 8 8 -54% -56% -37% 9 13 -71% -71% -63%

These results show that the addition of chromium, in a range of contents according to the invention, makes it possible to significantly reduce the absorption coefficient at each of the wavelengths of 1050, 950 and 850 nm, and therefore generally, to reduce the absorption of near infrared radiation.

Claims (13)

1. Glass sheet having a composition that comprises, in a content expressed in percentages by total weight of glass: SiO₂ 60 - 75% Al₂O₃ 0 - 4% B₂O₃ 0 - 4% Na₂O 5 - 20% CaO 1 - 15% MgO 0 - 10% K₂O 0 - 10% BaO 0 - 5% Total iron (expressed as Fe₂O₃) 0.002 - 0.02% characterized in that said composition comprises a chromium content such that: 0.0001% < Cr₂O₃ < 0.002%, expressed in percentages by total weight of glass, and a Fe²⁺ content, expressed as FeO, of less than 20 ppm.
2. Glass sheet according to the preceding claim, characterized in that the composition has a chromium/total iron ratio such that: 0.05 ≤ Cr₂O₃/Fe₂O₃ ≤ 1.
3. Glass sheet according to the preceding claim, characterized in that the composition has a chromium/total iron ratio such that: 0.1 < Cr₂O₃/Fe₂O₃ ≤ 1.
4. Glass sheet according to one of the preceding claims, characterized in that the composition comprises a chromium content such that: 0.0005% ≤ Cr₂O₃ < 0.002%.
5. Glass sheet according to one of the preceding claims, characterized in that the composition comprises a chromium content such that: 0.001% < Cr₂O₃ < 0.002%.
6. Glass sheet according to one of the preceding claims, characterized in that it has a coefficient of absorption at a wavelength of 1050 nm of less than or equal to 5 m^-1.
7. Glass sheet according to the preceding claim, characterized in that it has a coefficient of absorption at a wavelength of 1050 nm of less than or equal to 3.5 m^-1.
8. Glass sheet according to the preceding claim, characterized in that it has a coefficient of absorption at a wavelength of 1050 nm of less than or equal to 2 m^-1.
9. Glass sheet according to one of the preceding claims, characterized in that it is coated with at least one anti-fingerprint layer or has been treated so as to reduce/avoid marks made by fingerprints.
10. Screen or panel or pad, comprising at least one glass sheet according to one of Claims 1 to 9, said glass sheet defining a touch surface.
11. Screen or panel or pad according to the preceding claim, using FTIR or PSD optical technology.
12. Use of a glass sheet according to one of Claims 1 to 9 in a device using infrared radiation propagating essentially within said sheet.
13. Use according to the preceding claim, characterized in that the propagation of the infrared radiation is by total internal reflection.